ABSTRACT: Novel adoptive T cell therapies have enabled long lasting objective clinical responses in a significant proportion of patients with metastatic melanoma. Treatment efficacy and availability could be further improved by ex vivo genetic modification of lymphocytes allowing generation of large numbers of cells with enhanced anti-tumor function. The development of such adoptive cell transfer immune therapies is critically dependent on the availability of tools to track the distribution of genetically modified lymphocytes following transplantation in melanoma patients. Work by Program Project Grant (PPG) Investigators in animal models of cancer and in humans has demonstrated that this goal could be accomplished using novel molecular imaging techniques such as Positron Emission Tomography (PET). To visualize the distribution of genetically modified T lymphocytes and Hematopoietic Stem Cells transplanted in melanoma patients, these cells will be engineered to express a PET reporter gene derived from the Herpes Simplex Virus 1 thymidine kinase (HSVI-tk). HSVI-tk has been used extensively in clinical trials as a suicide gene and has a very high affinity for the PET probe (9-[4-[(18)F]fluoro-3-(hydroxymethyl)-butyl]guanine) (9(18)'F]FHBG). [9(18)F]FHBG administered in trace amounts accumulates specifically in cells expressing HSVI-tk and resulting signals can be detected by PET. We will use this technique for in vivo counting of genetically modified cells at various sites throughout the body, including lymphoid organs and metastatic melanoma deposits. Such measurements cannot be performed using conventional technologies and could provide eariy prediction markers for therapeutic responses. To support imaging studies by PPG Investigators, we propose to establish a Biological Imaging Core for noninvasive monitoring of immune responses. This Core will complement state-of-the-art 'in vitro' immUne monitoring measurements described in Core A and will enable PPG Investigators to pertorm preclinical and clinical 'in vivo' immune monitoring studies using multiple imaging modalities. The proposed Core will take advantage of the unique expertise and infrastructure for functional and anatomical tomographic imaging already available at UCLA and will also coordinate preclinical imaging experiments performed at other participating institutions. We envision that the Imaging Core will help cement long-term interactive multi-institutional collaborations involving experts in imaging, gene therapy, basic and clinical immunology, who are at the forefront of cancer immunotherapy transitional research.